In a fuel cell system, a combustible gas or synthesis gas containing hydrogen is generated by partial oxidation in a reformer, and this gas is then supplied to the anode of a fuel cell for conversion to electricity. The gases entering the catalytic converter in the reformer in partial catalytic oxidation include essentially hydrocarbons, air, water vapor, carbon monoxide and carbon dioxide. To avoid unnecessary monitoring of the incoming gas with regard to its composition, i.e., to be able to operate the process in the broadest possible lambda window, the anode exhaust gas of the fuel cell or the exhaust of one of the residual gas burners downstream from the fuel cell may be recycled to combine the anode gas and the cathode gas. This increases the water content in the gas, which contributes toward preventing the formation of soot.
In principle, a catalytic converter element operates at very high temperatures, often near the decomposition limit of the support material forming the catalytic converter element and the coating arranged thereon. On admission of the gas mixture consisting of the aforementioned components, an exothermic oxidation reaction takes place in the first few millimeters of the substrate, i.e., the support material, which has been coated with a catalytically active coating, the so-called “wash coat”; in this reaction, the hydrocarbons react with the oxygen to form carbon dioxide and water. In the remaining course, i.e., as the gas continues to flow through the catalytic converter element, an endothermic steam reforming process takes place, in which carbon dioxide and hydrogen are formed from carbon monoxide and water vapor. The highly exothermic reaction at the point of admission of the catalytic converter element, however, reduces the lifetime of the catalytic converter element and in particular the coating because the dissipation of heat toward the outside is very minimal at the center of the catalytic converter element, for example, and therefore the high temperatures that occur due to the exothermic reaction can in the long run have an effect on the coating, i.e., the wash coat.